1. Field of the Invention
The present invention relates to a plasmon generator for a thermal assisted magnetic recording head and a magnetic recording element that is equipped with the plasmon generator, and particularly relates to a configuration of the plasmon generator.
2. Description of the Related Art
Recently, in a magnetic recording apparatus typified by a magnetic disk apparatus, there has been a need for performance improvement of a thin film magnetic head and a magnetic recording medium in association with high recording density. As the thin film magnetic head, a composite type thin film magnetic head is widely used in which a reproducing head having a magnetoresistive effect element (MR element) for reading, and a recording head having an induction-type electromagnetic transducer element for writing, are laminated on a substrate.
The magnetic recording medium is a discontinuous medium in which magnetic grains are aggregated, where each magnetic grain has a single magnetic domain structure. Each recording bit on the magnetic recording medium is configured with a plurality of magnetic grains. In order to enhance the recording density, the unevenness of a boundary between recording bits that are adjacent to each other has to be smaller, and the magnetic grains have to be reduced in size for this purpose. However, small magnetic grains, i.e., magnetic grains with small volumes, cause a reduction in thermal stability of magnetization. In order to solve this problem, it is effective to increase anisotropy energy of the magnetic grains. However, high anisotropy energy of magnetic grains enhances a coercive force of the magnetic recording medium, and makes it difficult to record information with an existing magnetic head.
As a method for solving this problem, a so-called thermal assisted magnetic recording is proposed. In this method, a magnetic recording medium with greater coercive force can be used. When information is recorded, a magnetic field and heat are simultaneously added to a portion in the magnetic recording medium where information is recorded, and temperature of the portion is increased. With this process, information is recorded to the portion where the coercive force has been decreased by the magnetic field. Hereafter, a magnetic head that is used in the thermal assisted magnetic recording is referred to as a thermal assisted magnetic recording head (TAMR head).
A conventional TAMR head includes a core that propagates light irradiated from a laser diode and a plasmon generator that generates near-field light (NF light). The plasmon generator is coupled with a portion of propagation light that propagates in the core in a surface plasmon mode and generates a surface plasmon, allows the surface plasmon to propagate up to a front end surface positioned on an air bearing surface, and generates the NF light on the front end surface.
In the conventional TAMR head, deterioration of recording properties (such as an S/N ratio) in association with continuous recording occurs. Agglomeration of the front end surface of the plasmon generator is recognized as a main factor. Agglomeration is a phenomenon where metal atoms are gathered, and occurs as a result of dispersion or movement of the metal atoms using heat and stress as a driving force. Asperities exist on the air bearing surface of a magnetic head slider and a surface of the magnetic recording medium, and the front end surface of the plasmon generator may contact the magnetic recording medium while the magnetic recording apparatus is in operation. Temperature increase and stress increase due to the impact that occurs at this time cause agglomeration. The agglomeration easily causes the front end surface of the plasmon generator to recess from the air bearing surface. As a result, the distance between the plasmon generator and the magnetic recording medium is increased, and the capability to heat the magnetic recording medium is decreased over time, which causes deterioration of the S/N ratio. Therefore, it is desired to suppress agglomeration of the plasmon generators to ensure the reliability of the TAMR head.
US 2014-0043948 discloses a plasmon generator that consists primarily of Au, and where Co and Fe are added in a ratio of 0.2 at % to 2.0 at %. Agglomeration is suppressed by adding Co and Fe. However, an Au alloy where Co and Fe have been added exhibits poor propagation efficiency of the surface plasmon. Consequently, heat generation occurs due to the propagation loss of the surface plasmon on the surface plasmon propagation region of the plasmon generator. As a result, reliability of the plasmon generator is reduced. In other words, the reliability for agglomeration and recess of the plasmon generator at the tip portion is improved, but the above effect is reduced because of the impact of the heat generation due to the propagation loss of the surface plasmon.
The objective of the present invention is to provide a plasmon generator that has high thermal reliability, and where the recess on the front end surface is minimal, with a magnetic recording element using the plasmon generator.